Use of PS-Zn-anthra complex as an efficient heterogeneous recyclable catalyst for carbon dioxide fixation reaction at atmospheric pressure and synthesis of dicoumarols under greener pathway

Article abstract of DOI:10.1016/j.jorganchem.2018.03.039

A polystyrene functionalized Zinc anthranilic acid complex catalyst has been prepared. The PS-Zn-anthra complex has been characterized by EDX, Scanning electron micrographs (FE-SEM), FTIR spectra, UV–vis spectra and thermogravimetric analyses. A greener a

Full text of DOI:10.1016/j.jorganchem.2018.03.039

Accepted Manuscript
Use of PS-Zn-anthra complex as an efficient heterogeneous recyclable catalyst for
carbon dioxide fixation reaction at atmospheric pressure and synthesis of dicoumarols
under greener pathway
Swarbhanu Ghosh, Paramita Mondal, Debasis Das, Kazi Tuhina, Sk. Manirul Islam
PII:
S0022-328X(18)30210-9
10.1016/j.jorganchem.2018.03.039
JOM 20389
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 20 August 2017
Revised Date: 24 March 2018
Accepted Date: 27 March 2018
Please cite this article as: S. Ghosh, P. Mondal, D. Das, K. Tuhina, S.M. Islam, Use of PS-Zn-anthra
complex as an efficient heterogeneous recyclable catalyst for carbon dioxide fixation reaction at
atmospheric pressure and synthesis of dicoumarols under greener pathway, Journal of Organometallic
Chemistry (2018), doi: 10.1016/j.jorganchem.2018.03.039.
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ACCEPTED MANUSCRIPT
Use of PS-Zn-anthra complex as an efficient heterogeneous recyclable catalyst for
Carbon dioxide fixation reaction at atmospheric pressure and synthesis of dicoumarols
under greener pathway
Swarbhanu Ghosha‡, Paramita Mondala,b‡ , Debasis Das*b, Kazi Tuhinac and Sk.
*
Manirul Islam a
aDepartment of Chemistry, University of Kalyani, Kalyani, Nadia, 741235, W.B., India
bDepartment of Chemistry, The University of Burdwan, Burdwan, West Bengal, India
cDepartment of Chemistry, B.S. College, Tangra Khali, Canning, S-24 PGS, West
Bengal, India
Abstract
A polystyrene functionalized Zinc anthranilic acid complex catalyst has been prepared.
The PS-Zn-anthra complex has been characterized by EDX, Scanning electron micrographs
(FE-SEM), FTIR spectra, UV-vis spectra and thermogravimetric analyses. A greener and
novel methodology was considered for the production of dicoumarol derivatives utilizing PS-
Zn-anthra complex as a Lewis acid catalyst, non-toxic, mild in H2O employing
heteroaromatic/aromatic aldehydes and 4-hydroxycoumarin. The catalyst also shows good
catalytic activity in the cyclo addition of CO2 to epoxide. The results of activity of catalyst
imply that the procedure adopted provides numerous advantages such as low loading of
catalyst, operational simplicity, mild reaction conditions, quantitative yields, and short
reaction time. The PS-Zn-anthra complex exhibited the elevated efficiency of recycling in
these reactions. This catalyst can be recycled for five times without appreciable loss of its
activity.
Keywords: Heterogeneous Catalyst, PS-Zn-anthra complex, Cyclic Carbonate,
4-hydroxycoumarin, aromatic/heteroaromatic aldehydes, dicoumarols
‡ These authors contribute equally to this manuscript.
*Authors to whom correspondence should be addressed.

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Prof. S. M. Islam, Department of Chemistry, University of Kalyani, Kalyani, Nadia,
741235, W.B., India. Phone: +91-33-2582-8750, Fax: +91-33-2582-8282, e-mail:
manir65@rediffmail.com
1.Introduction
CO2 is an extremely substantial C1 feedstock in the synthetic field of organic
chemistry as it is cost-effective, non-hazardous, non-flammable and abundant in nature [1].
The global warming caused by the unlimited utility of fossil fuels, other activities of human
and industrialization and to minimize it is the challenging area of current interest. In the
present day, huge attention has been paid in order to establish the hazardless procedures
which are environmentally benign based on reactions of CO2 fixation [2-6]. Greater than
thirteen gigatonnes of CO2 produced yearly from the fossil fuels burning for the generation of
electrical energy and heat, is a most important supplier to climate change and acidification of
seawater [7]. It has been predicted by the IPCC (International Panel for Climate Change) that
by the year 2100, the average universal temperature could increase by as high as 1.8-1.9°C
[8]. A decrease in emissions of green house gas affecting weather change is immediately
essential on a scale of the global system. One of the procedures towards decreasing emissions
of carbon dioxide is CCS (capture of carbon and storage), which has the potential to diminish
emissions of the future world from the use of energy by twenty percent [9]. But this method
(CCS) is less cost-effective compared to CCU (carbon capture and utilization) method
because of separation, purification and transportation of CO2. The economics of capturing
CO2 could be improved if the captured carbon could be utilized. This process generates more
revenue and some cases it reduces overall carbon emission. [10]. Nowadays, a wide series of
heterogeneous and homogeneous catalytic systems such as functionalized polymers [11],
crown ether [12], alkali metal salts [13], ionic liquids [14] or titanosilicates [15], organic
bases [16-17], mixed oxides [18,19], hydrogen bond donors [20,21], metal complexes [22],
zeolites [23,24], functionalized mesoporous materials [25-29] and zeolitic imidazolate
frameworks [30,31] are reported in CO2 transformation of various chemical systems.
Recently, a variety of metal-free tri-s-triazine terminal-linked ionic liquids [32], urea
derivative-based ionic liquids (UDILs) [33], and binary Zn-SBA-15/KI catalysts [34] were
generated with higher thermal stability. These catalysts were structurally examined as well as
applied to CO2 capture and transformation under the application of mild conditions.
Dicoumarol is a naturally occurring anticoagulant drug which uses as an antagonist
vitamin K. It is chemically designed as 3,3’-methylenebis[4-hydroxycoumarin] and derived

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from coumarin metabolism in the sweet clover (Melilotus officinalis and Melilotus alba) by
Penicillium jensi and Penicillium bacterial nigricans. A recent work has exhibited that the
hindrance of NAD (P) H: quinone oxidoreductase (NQO1) with dicoumarol affects the
damage of cell and oxidative strain in cancer pancreatic cells [35]. Such species have been
established in clinical trials to have some action against malignant melanoma, metastatic
renal cell carcinoma and prostate cancer [36–38]. Lanthanum(III) complexes of dicoumarol
have been found to exhibit cytotoxic activity widely [39]. Species having this ring also
imparts different other activities of the pharmacological system such as anthelmintic, HIV
proteases inhibition, antioxidant, insecticidal, antifungal, hypnotic, antimicrobial and
phytoalexin [40–47]. A number of schemes have been known for the production of this
significant group of compounds during the last decades including utility of (Et2AlCl3) [48],
DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) [49], molecular iodine [50], refluxing ethanol or
acetic acid [51], manganous chloride [52], thermal solvent-free reaction conditions [53] and
POCl3 in dry DMF [54] etc. Despite their potential values, various reported procedures
experience some disadvantages such as expensive reagents, long reaction time, stringent
conditions, use of toxic catalysts that are detrimental to the environment and low product
yields. In order to overcome these limitations, the development of new procedure are required
for the generation of dicoumarol in terms of catalyst reusability, economic viability and
operational simplicity. Reactions catalyzed by organic Lewis-acid in water have attracted
much attention in organic synthesis as they allow access to more environmentally-benign
processes under mild reaction conditions.
Polystyrene is the most usually known heterogeneous support due to its high stability
in the environment and low cost. The polymer-supported zinc catalysts are obtained from
Merrifield Resin, have worked in different coupling reactions [55-63], and minor leaching of
zinc has appeared during the time of cross-coupling.
In the current study, we have synthesized polymer-supported Zn catalyst and
utilized it in the production of dicoumarol derivatives. The characterization of polymer-
supported Zn catalyst was done by different spectroscopic and physicochemical techniques.
The impact of the different parameters on the catalytic activity was checked. The most
remarkable character of the polymer-supported Zn catalyst involves fast reactions with
outstanding transformation and absolute stability under the application of different reaction
conditions. Moreover, the Zn catalyst displayed excellent recyclability for the production of
dicoumarol derivatives [64].
2. Experimental Section

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All chemical reagents were analytical grade. Purification of all solvents was done and
dried according to standard methods. Merrifield resin was bought from Sigma-Aldrich and
Zinc(II)chloride was purchased from Arora Matthey. Other chemicals were bought from Alfa
aesar (India) and Merck.
2.1. Materials
2.2. Characterization Techniques
A Perkin Elmer, 2400C, USA elemental analyzer was utilized to assemble
microanalytical data (C, N and H). Analysis of surface morphology of functionalized
polystyrene supported ligand and metal complex was performed with a scanning electron
microscope (ZEISS EVO40, England) equipped with a facility of EDX. FTIR (Fourier
transform infrared) spectra for the catalyst precursors and catalyst were recorded on a Perkin
Elmer, FTIR 783, USA spectrophotometer using KBr pellets. UV-vis spectrum was recorded
on a Shimadzu, Japan, UV-2401PC double beam spectrophotometer equipped with an
integrating sphere attachment for solid samples. The thermal stability of the immobilized
catalyst was determined with a Mettler Toledo, Switzerland, TGA/DTA 851e instrument. All
reaction products were identified by using 1H NMR spectra.
2.3. Synthesis of PS-Zn-anthra complex
The synthetic method of PS-Zn-anthra complex is given in Scheme 1. The complex
was prepared according to the literature method [65]. Initially, the Merrifield resin (1) (500
mg) was reacted with anthranilic acid (250 mg) in DMF (5 mL) under the application of
reflux condition for 32 h to give polymer-anchored ligand (2). This polymer-anchored ligand
(1 g) consequently reacted with ZnCl2 (0.1 g) in ethanol (10 mL) for 10 h at 70 oC to produce
the resultant polymer supported Zn catalyst (3).

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Scheme 1. Preparation of PS-Zn-anthra complex
Elemental analysis of PS-Zn-anthra complex by ICP spectroscopy provided a zinc loading of
4.1 wt%. Elemental analysis of PS-Zn-anthra complex provided presence of 3.74 wt% Cl.
The calculated molar Cl/Zn ratio of 1.1 is in agreement with that expected for structure (3)
[(PS-anthra)ZnClL]. Additionally, Elemental analysis revealed the presence of 1.12 wt% N
corresponding to a molar N/Zn ratio of 1.2. Within the limit of uncertainty of elemental
analysis (± 10%), this value is almost identical with expected (N/Zn = 1) based on the
structure (3). Elemental analysis significantly revealed the presence of 2.42 wt% Cl (i.e
elimination of 1.32 wt% Cl in ligand from 3.74 wt% Cl in complex) in PS-Zn-anthra
complex. 2.42 wt% Cl in PS-Zn-anthra complex significantly came from Zinc chloride. This
elemental analysis allowed for the determination of a molar Cl/Zn ratio of 1.1 for structure
(3) [66, 67].
Table 1. Chemical composition polymer-anchored ligand and its Zn catalyst.
Compound
Colour
C (%)
H (%) N (%) Cl (%)
Zn
Loading(%)
PS-anthra ligand
Pale yellow
Pale yellow
83.27
80.43
7.34
7.22
4.23
1.11
1.32
3.74
-
PS-Zn-anthra complex
4.09
2.4. Typical procedure for synthesis of cyclic carbonates at 1 atmospheric pressure of
CO2

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Oxirane (5 mmol), TBAB (Bu4NBr) (0.083 mmol, 26.7 mg) and PS-Zn-anthra complex
(50 mg) were poured into a 100 ml R.B flask placed on a magnetic stirrer. The R.B flask was
fitted with a stopper pierced by a CO2 balloon under 1 atm pressure. The reaction mixture
was stirred at room temperature for 6 h. The transformation of oxirane to the respective
1
organic five-membered carbonate was checked from the data of H NMR spectra. The
isolation of organic five-membered carbonate was performed by column chromatography.
The characterization of the products was analyzed from the concept of their spectroscopic
data (1H NMR) and was confirmed by comparison of NMR spectra with literature data.
2.5. Typical method for the production of dicoumarols
A mixture of aldehyde (1 mmol), PS-Zn-anthra complex (5 mol%), 4-hydroxycoumarin (2
mmol), and water (5 mL) was poured in a R.B. flask and refluxed at 100oC for the fixed time.
The progress of the reaction was checked by TLC (thin-layer chromatography). At the end of
the reaction, the solution was cooled to RT. The resultant product was extracted with DCM,
dried over anhydrous sodium sulphate, and resultant solution was concentrated to provide.
The PS-Zn-anthra complex was separated from the reaction mixture by easy separation of
organic and aqueous phases. The PS-Zn-anthra complex present in the layer of the aqueous
phase was separated by precipitating the layer of aqueous phases by addition of acetone and
utilized for the successive cycle.
3. Results and discussion
3.1. Characterization of PS-Zn-anthra complex
3.1.1. Microscopic analysis
Scanning electron micrographs (SEM) of the polymer-anchored ligand and the PS-Zn-
anthra complex were recorded to recognize the change of morphology occurring on the
polymer matrix surface. In Fig. 1 the SEM images of the polymer-supported ligand (a) and
the PS-Zn-anthra complex (b) are demonstrated. SEM image exhibited a difference in
morphology between PS-anthra ligand and the PS-Zn-anthra complex. EDX data established
the attachment of metal on the polymer matrix surface (Fig.2). There is no change in
morphology between PS-Zn-anthra complex and reused PS-Zn-anthra complex.

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Fig.1. FE-SEM picture of PS-anthra ligand (a) and PS-Zn-anthra complex (b) respectively.
Fig. 2. EDX spectra of PS-anthra ligand (A) and PS-Zn-anthra complex (B).
3.1.2.Thermogravimetric analysis:
Thermogravimetric analyses of PS-Zn-anthra complex and PS-anthra ligand, polymer
supported anthranilic acid, were taken in air atmosphere at a heating rate of 10 oC min-1. PS-
o
o
Zn-anthra complex is stable up to 430 C whereas PS-anthra ligand decomposes at 390 C
(Fig. 3). After coordination with Zn, the thermal stability of PS-anthra ligand is slightly
enhanced. Study of DTA supports that the stages of decomposition are exothermic in nature
(not shown).

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120
100
80
60
40
20
0
PS-anthra ligand
PS-Zn(II)-anthra complex
100
200
300
400
500
600
Temperature (oC)
Fig. 3. Thermogravimetric analyses of PS-anthra ligand and PS-Zn-anthra complex
3.1.3. UV-visible spectra of the PS-Zn-anthra complex:
The UV-vis spectra indicated further confirmation for the existence of Zn supported on
polymer. The UV-vis spectra of the Zn catalyst on polymer support has been performed in
reflectance diffused spectrum mode as a disc of BaSO4 owing to limitations of its solubility
in ordinary organic solvents. Fig.4 indicates the UV–vis reflectance diffused spectra
produced porous PS-Zn-anthra complex. The UV–vis reflectance diffused spectrum of PS-
Zn-anthra complex appeared at absorption band at 251 nm. The UV-visible spectrum of PS-
anthra ligand and its PS-Zn-anthra complex is shown in Fig.4. The characteristic bands at
230, 251, 342 nm for the pure ligand are due to the π-π* transition (see supporting
information). When PS-anthra ligand was coordinated with Zn, the disappearance of the
band at 342 nm occurs and appearance of the new band at 370 nm is observed. It may be
assigned to the charge transfers between coordinated atoms and the central zinc atom. [68].

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PS-Zn(II)-anthra complex
0.35
0.30
0.25
0.20
0.15
0.10
0.05
200
300
400
500
600
700
Wavelength in nm
Fig. 4. The UV-visible absorption spectrum of PS-Zn-anthra complex.
3.1.4. FT IR spectra:
The attachment mode of anthranilic acid and Zn onto the polymer support is established
by spectral IR data both in the far (600-50 cm-1) and mid (4000-400 cm-1) IR regions. The
pure Merrifield resin beads exhibit a characteristic IR sharp peak at 1258 cm-1 (ν -CH2-Cl
group in Merrifield resin). Appearance of a strong band at 3456 cm-1 (ν-NH, secondary
amine) and disappearance of (ν-C-Cl) band on coordinating with anthranilic acid implies the
formation of covalent bond through N atom. Other peaks at 1702 (ν C=O), 3449 (ν -OH),
1410 (νsym COO) and 1560 (νasym COO) confirmed the ligand formation [69]. After
coordination with metal, shifting of peaks towards higher wavelength regions (1405 νsym
–
COO, 1556 νasym –COO and 3280 ν N-H) implies the participation of the –NH2 and COOH
groups of the anthranilic acid in formation of complex.

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Figure 5. FT IR spectra of the PS-anthra ligand(a) and PS-Zn-anthra complex(b).
3.2.CatalyticActivity
3.2.1. Organic cyclic carbonates synthesis catalyzed by PS-Zn-anthra complex
CO2 incorporation on oxiranes leads to the production of organic cyclic carbonates over
PS-Zn-anthra complex with TBAB (Bu4NBr) as cocatalyst as shown in Scheme 2.
Scheme 2. Generation of organic cyclic carbonates from CO2 and oxiranes
All the conditions have been screened including time of reaction, the quantity of Bu4NBr to
optimize the product yield of the cyclic five-membered organic carbonate (Table 2). The
incorporation of CO2 on SO (styrene oxide) to SC (styrene carbonate) is specified as the
model reaction (Table 2). During the preliminary work, the quantity of Bu4NBr (TBAB) has
been altered to catalyze this carbon dioxide fixation. High yield of styrene carbonate was
obtained using 5 mol% TBAB (Table 2, entries 8). From the table 2, time of reaction has the
very essential role in the product yield (Table 2, entries 4-9). The advancement of reaction
has been examined even at the tiny time period and obtained moderately better yields. When
reactions took place with lesser and higher than 5 mol% of TBAB (Bu4NBr), incomplete SO

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conversions and comparatively lesser yield were observed (Table 2, entry 1-3). It was also
investigated that without cocatalyst and PS-Zn-anthra complex small quantity of expected
product was observed (entries 9,10). Under optimized conditions of the reaction of TBAB
(5 mol%) at room temperature for 6 h with just catalyst (50 mg) at 1 atmospheric CO2
pressure, 97% yield of SC was observed (Table 2, entry 8).
Table 2. Optimization of conditions of reaction for the production of oxirane (styrene
carbonate)a
Entry
TBAB /
CO2/atm
Time
(h)
Yieldb
(%)
TON/TOF
Bu4NBr
(h-1)
(mol%)
1
2
5
5
2
4
5
6
5
5
5
0
1
1
1
1
1
1
1
1
1
1
4
5
6
6
6
6
2
3
6
6
82
91
131/33
145/29
41/7
3
26
4
62
99/16
155/26
122/20
92/46
118/39
-
5
97
6
77
7
58
8
9c
74
Trace
10
Trace
-
aReaction conditions: Oxirane (5 mmol of SO), PS-Zn-anthra complex (3.135 x 10-5 mol),
b
room temperature; GC yield of cyclic carbonate; cwithout catalyst
For exploring the total potential of PS-Zn-anthra complex in the carbon dioxide fixation
the reaction time has been enhanced under optimized conditions of reaction until the entire
transformation of SO is observed. Figure 6 explored the idea for the time of reaction with
transformation and selectivity. The plot indicated the transformation of oxirane (styrene
oxide) enhances linearly over the function of time from the beginning to 6 h and it kept the

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conversion level of 97% yield in subsequent 2 h, whereas the SC selectivity kept 100%
approximately at the whole reaction period. From Figure 6 it is clear that time of reaction of 6
h is satisfactory to undergo this cycloaddition reaction at normal temperature.
Figure 6. Influence of time of reaction on the transformation of SO to SC over PS-Zn-anthra
complex
To study the possibility of applying the Zn catalyst for the chemical fixation of CO2 with
different epoxides such as allyl glycidyl ether, epichlorohydrin, propylene oxide, styrene oxide
and glycidol (epoxides with substituted functional groups), aryloxy epoxides (1, 2-epoxy-3-
phenoxy propane) have been used as substrates under the application of optimized conditions.
The investigational results are listed in Table 3. The transformation of all the oxiranes to five-
membered organic cyclic carbonate derivatives via chemical fixation undergo simply with
elevated yield and exceptional selectivity. Further attempt to conduct the chemical fixation at
o
the ideal atmospheric pressure, failed, as propylene oxide with a boiling point of 34 C
partially evaporated into the balloon at room temperature and did not participate in the
cycloaddition reaction (Table 3, entry 3) [70]. It is experimental that electron-withdrawing
groups (Table 3, entry 6) and electron-donating (Table 3, entries 1, 3 and 4) on terminal
epoxides has no effect on the yields of cyclic carbonates.
Table 3. Production of cyclic organic five-membered carbonates over PS-Zn-anthra complex
under the application of optimized conditions.

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Entry
1.
Epoxide
Product
Time Yielda TON/TOF
(h)
(%)
(h-1)
6
96
153/25
6
6
97
90
155/26
143/24
2.
3.
6
97
155/26
4.
5
5
89
94
141/28
149/30
5.
6.
aGC yield of five-membered organic carbonate. 1H NMR spectra of the cyclic carbonate are
provided in the supporting information.
The plausible mechanistic pathway for the generation of organic carbonate through the
reaction of CO2 and oxiranes over PS-Zn-anthra complex is shown in Figure 7. The active
sites of PS-Zn-anthra complex activate the oxiranes through non-covalent interaction with the
oxiranes O atoms, whereas the basic site present at the surface owing to amine can activate
the molecules of CO2 gas.

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Figure 7. Probable mechanistic pathway for the formation of cyclic carbonates over PS-Zn-
anthra complex.
As seen from Figure 7, the formation of a halo-alkoxide is observed through the
interaction of PS-Zn-anthra coordinated oxirane with Bu4NBr. Then the incorporation of CO2
occurs through the bond of metal alkoxide system and generates a metal hemicarbonate
[reference], which results in ring-closer to yield the organic carbonate along with the onium
halide again. The synthetic step of cyclic carbonate undergoes via intra-molecularly rather
than inter-molecularly and this could be attributed to the excellently elevated activity of the
catalyst of Zn-anthra complex.
3.2.2. Dicoumarol synthesis catalyzed by PS-Zn-anthra complex
The plan of the current work was to sketch an effective procedure for PS-Zn-anthra
complex catalyzed the reaction between a variety of aromatic/heteroaromatic aldehydes and
4-hydroxycoumarin to produce the derivatives of resultant dicoumarol with outstanding yield
(93–98%) in a short time periods (3–5 min) (Table 7). Our first examinations were concerned
with the PS-Zn-anthra complex catalyzed the reaction between 4-hydroxybenzaldehyde and
4-hydroxycoumarin as a model reaction. The advancement of reaction was conducted under
different the reaction conditions in order to optimize solvents and catalysts conditions and the
results are recorded in Tables 5 and 6. It was expected that the best results were observed for
H2O, which is an advantageous solvent from the viewpoint of green chemistry. These

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outstanding initial results made us thoughtful to further investigate the catalyst applicability
for the production of other derivatives of dicoumarol moiety (Scheme 3 and Table 4).
Scheme 3: Production of derivatives of dicoumarol moiety using the Zn catalyst in H2O
Reactivity of 4-Hydroxycoumarin ring at position 3 is high owing to the existence of
an electron releasing hydroxyl group at position 4 and an electron attracting C=O group at
position 2. PS-Zn-anthra complex has not been utilized so far as a potential catalyst to
produce dicoumarol derivatives. This encouraged us to check the efficiency of the catalyst to
produce dicoumarol derivatives. As the lone pair of electrons from the oxygen atom of the
hydroxyl group and the C=C bond are in conjugation, this creates the ring of coumarin
moiety very suitable at C-3 to react with C=O carbon of the aldehydes. The reaction
mechanism has been demonstrated to produce different dicoumarols using PS-Zn-anthra
complex as catalyst (Scheme 3). In the beginning, the condensation of 4-hydroxy coumarin
and 4-methoxy benzaldehyde was applied for trial as a model reaction to produce the
dicoumarol derivatives using PS-Zn-anthra catalyst in water in a water bath at 100 oC. A wide
series of dicoumarols have been produced.
In the present study of catalyst loading, the influence of the relative quantity of Zn
catalyst on the result of the model reaction was observed. The best yield was observed with
the utilization of catalyst (5 mol%). When the progress of the reaction was observed by
utilizing less than 5 mol% (i.e. 1 mol % , 2 mol % and 4 mol %) of Zn catalyst, the progress
of reactions was either took long time periods to complete or incomplete.
Table 4. Optimization of conditions of the reaction in production of (1) using different
quantity of PS-Zn-anthra catalyst under reflux in H2O.

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Entry
1.
Catalyst
Time (min)
Yield (%)
PS-Zn-anthra (1 mol%)
PS-Zn-anthra (2 mol%)
PS-Zn-anthra (4 mol%)
PS-Zn-anthra (5 mol%)
3
3
3
3
29
37
79
98
2.
3.
4.
aReaction conditions: aldehyde (1 mmol), 4-hydroxycoumarin (2 mmol), H2O (15 mL) and
100oC.
In a relative study, various types of catalysts were utilized to exhibit the advantage of
PS-Zn-anthra complex over other catalysts. General Lewis acids of different transition metals
were utilized for the model reaction (Table 5). Our examination exhibited that the activity of
catalyst of different transition metal chlorides was seen to be of the order PS-Zn-anthra
complex > AlCl3 > NiCl2 > CuCl2 > FeCl3 > ZnCl2. Initial investigation implies that PS-Zn-
anthra complex was better than other catalysts in terms of reaction time and yield. When the
progress of the reaction was investigated with AlCl3, NiCl2, CuCl2 the reaction was
accomplished in comparatively short time (20–30 min) and the yield of product was obtained
in good to moderate amount, but these homogeneous catalysts are difficult to separate from
the reaction mixture. The product was generated in small yields using ZnCl2, FeCl3 and L-
Proline whereas formation of product was not found when the progress of reaction took place
in p-toluene sulfonic acid (PTS). From Table 5 it is noticed that PS-Zn-anthra complex
exhibited the maximum activity with regard to the conversion of 4-hydroxycoumarin to
dicoumarol.
Table 5 Influence of different catalysts and catalyst loading on the production of dicoumarol
(entry 1c)a
Entry
1
Catalyst
Time
3 min
Yieldb (%)
98
PS-Zn-Anthra Complex

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2c
3d
4d,e
PS-Zn-Anthra Complex
20 min
20 min
30 min
20 min
20 min
30 min
20 min
20 min
30 min
5 min
87
64
PS-Zn-Anthra Complex
PS-Zn-Anthra Complex
AlCl3
51
5
6d
7d,e
8d
91
AlCl3
56
AlCl3
41
NiCl2
42
9
NiCl2
79
10
11
12d
13d,e
14
15
16
CuCl2
51
Zn(Proline)2
Zn(Proline)2
Zn(Proline)2
FeCl3
96
20 min
30 min
30 min
24 h
58
45
21
ZnCl2
11
No Catalyst
24 h
Trace
a Reaction conditions: aldehyde (1 mmol), 4-hydroxycoumarin (2 mmol), water (15 mL),
100oC and PS-Zn-anthra (5 mol%). b All yields correspond to isolated products.c Catalyst
loading was 1 mol%. d Catalyst loading was 0.5 mol%. e Ethanol was used in place of water.
To contrast, the efficiency as well as capability of the reaction under aqueous
conditions, the examination of model reaction, was performed in the existence of PS-Zn-
anthra complex in various solvents such as CH3CN, CH2Cl2, H2O and EtOH (Table 3). The
utilization of a comparatively less aprotic polar solvent, CH2Cl2, generated the product in
extremely low yield after a long time period (Table 6, entry 4). With the utilization of aprotic
solvents of comparatively high polarity, such as MeCN (Table 6, entry 3), either formation of
trace product was found or no reaction was observed. In protic polar solvents EtOH high
yield was observed under reflux conditions but it required a longer reaction time of long-
range, within 30 min (Table 6, entries 2). When the progress of the reaction was examined in
H2O, the resultant product was observed in high yield in 3 min (Table 6, entry 1). It was
expected that the most excellent results were found for H2O, which is an attractive solvent in
green chemistry.
Table 6 Influence of solvent on the production of dicoumarol (entry 1c) in the presence of
PS-Zn-anthra complex (5 mol%)

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Entry
1.
Solvent
H2O
Timea
3 min
30 min
48 h
Yieldb (%)
98
84
2.
EtOH
3.
Acetonitrile
DCM
Trace
46
4.
48 h
a All the reactions were checked by thin layer chromatography. b All yields correspond to
isolated products.
An attractive trend was obtained which made our option of the reaction medium,
straightforward and very simple among the three protic solvents tried. With the rise in
dielectric constant the PS-Zn-anthra complex was observed to provide higher yield in
smaller time, and when plot of % yield/Minute against the dielectric constants of the solvents
was generated, it exhibits a relationship of the monotonic system between the two (Fig. 8.).
Fig.8. Comparative efficiency of some solvents which are protic in nature as medium of
reaction for synthesis of the dicoumarol moiety with PS-Zn-anthra complex.
The character of the aromatic group was no considerable influence on the rate of
reaction or yield of the product. Instead of some organic solvents, the utility of H2O is more
significant due to its cheapness and safety. The scheme 3 shows a proposed mechanism to
produce by PS-Zn-anthra complex.

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Table 7. Reaction between aromatic/heteroaromatic aldehydes and 4-hydroxycoumarin
catalyzed by a PS-Zn-anthra catalyzed complex in H2O.a
Entry
Aldehyde
Product
Timeb/min Yieldc TON/TOF
(%)
(h-1)
1a
4
94
89/1335
1b
1c
5
3
93
98
88/1056
93/1860
1d
1e
1f
5
5
3
94
97
96
89/1068
92/1104
91/1820

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1g
1h
3
4
98
96
93/1860
91/1365
1i
1j
5
4
94
96
89/1068
91/1365
aReaction conditions: aldehyde (1 mmol), 4-hydroxycoumarin (2 mmol), water (15 mL),
b
c
100oC and PS-Zn-anthra (5 mol%). All the reactions were checked by TLC. All yields
correspond to isolated products.
The plausible mechanism for the formation of dicoumarol from 4-hydroxycoumarin
and aldehydes catalysed by PS-Zn-anthra complex is shown in Figure 9. The significance of
PS-Zn-anthra complex is highly observed for the formation of dicoumarol. Position 3 of
4-Hydroxycoumarin moiety is extremely reactive owing to the existence of an electron
releasing hydroxyl group and an electron attracting C=O group. A lone pair of electrons from
oxygen and the existence of a C=C double bond constructs the 4-hydroxycoumarin ring very
suitable at position 3 to react with the C=O of aldehydes to provide derivatives of dicoumarol
moiety [71, 72].

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Figure 9. Plausible mechanism for the production of Dicoumarol using PS-Zn-anthra catalyst
Figure 10. Another porposed mechanism for the production of Dicoumarol using PS-Zn-
anthra catalyst
3.3. Recyclability of PS-Zn-anthra complex
It is significant to examine the isolation, recoverability and recyclability for a
polystyrene supported catalyst. The PS-Zn-anthra complex executed outstanding reusability

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in the synthesis of the cyclic carbonate and dicoumarols synthesis (Fig.11). Catalyst reuse
and recovery are essential issues for cyclic carbonate synthesis and synthesis of dicoumarols.
Recycling in successive batch operations and easy catalyst separation can significantly
enhance the reaction efficiency. The PS-Zn(II)-anthra complex was recovered by easy
filtration and washed with ethyl acetate followed by acetone then dried out in low pressure at
50oC after the end of the reaction. The recovered catalyst was utilized for the next run with
the extra incorporation of substrates in proper quantity under optimum conditions of reaction.
The PS-Zn-anthra complex exhibits the fixed activity of catalyst up to five reaction cycles.
Deterioration of catalyst was not found, supporting the elevated stability of the catalyst with
heterogeneous nature under the application of reaction conditions.
Fig.11. Recycling efficiency of PS-Zn-anthra complex catalyst for cyclic carbonate synthesis
and synthesis of dicoumarols.
To explore the activity of PS-Zn-anthra complex and current method, the activity of
catalyst PS-Zn-anthra has been compared with a few other reported catalytic systems and
these are shown in Table 8. Compared to the some reported catalytic systems for the
production of organic five-membered cyclic carbonates under the application of CO2 and
synthesis of dicoumarols, our PS-Zn(II)-anthra complex exhibited more efficiency of the
catalyst under the application of optimization conditions [73-77].

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Table 8: Comparison of activity of the current catalyst (PS-Zn-anthra complex) in organic
five-membered carbonates preparation and the synthesis of dicoumarols with other reported
heterogeneous catalysts.
Reaction
Catalyst
Reaction condition
Yield (%)
Ref.
HBimCl-
Styrene epoxide (10mmol),
Cat. (0.1 g), PCO2 (1.5 Mpa),
Time – 5h, Temp. 1300C
Styrene epoxide (0.2 mol),
Cat. (0.17 g), PCO2 (2 Mpa),
Time – 5h, Temp. 1400C
Styrene epoxide (12.5 mol),
Cat. (50 mg), PCO2 (1 atm),
Time – 118(48) h, Temp.
29(50) 0C
96.1
73
Cyclic
NbCl5/HCMC
carbonates
synthesis
F-IRMOF-3
Co/POP-TPP
84
74
75
77.9
PS-Zn-anthra
complex
Styrene oxide (5 mmol),
catalyst (50 mg), PCO2 (1
atm), RT, Time- 6h
97
This
study
SAMSNs
Benzaldehyde (1 mmol), 4-
hydroxy coumarin (2 mmol),
cat.(0.025g), H2O (3 ml),
Time – 20 min, Temp. 800C
96
76
77
Dicoumarol
synthesis
H14[NaP5W30O110]/SiO2 Benzaldehyde (1 mmol), 4-
hydroxy coumarin (2 mmol),
95
cat.(0.025g),
EtOH-H2O
(1:1), Time – 5 h, Temp.
reflux
Benzaldehyde (1 mmol), 4-
hydroxy coumarin (2 mmol),
cat.(5 mol%), H2O (15 ml),
Time – 5 min, reflux
PS-Zn-anthra
complex
97
This
study

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4.Conclusions
In conclusion, the polystyrene-supported Zn complex has been prepared as an excellent
heterogeneous catalyst. The catalyst performed an exceptional activity for the production of
organic five-membered cyclic carbonates from oxiranes in presence of CO2 under
atmospheric pressure at RT and active transformation of dicoumarols using H2O as the
green solvent. An efficient and simple methodology has been effectively established for the
synthesis of a wide range of dicoumarols using PS-Zn-anthra complex as the recyclable
catalyst. The great activity of the catalyst of PS-Zn-anthra complex for these conversions
can be sustained by high yields of dicoumarols as well as the short time of the reaction. This
scheme is environmentally non-hazardous and may confirm useful to both industry and
academia for the change of socio-economic system.
Acknowledgements
SMI acknowledges the Department of Science and Technology, DST-SERB, (Project No
EMR/2016/004956), New Delhi, Govt. of India, Council of Scientific & Industrial Research,
CSIR, (Project No 02(0284)/16/EMR-II), Date: 06-12-2016; and Department of Science and
Technology, West Bengal (DST-W.B.) WB-DST (Sanc.)/ST/P/S&T/4G-8/2014, dated
04/01/2016; for financial support. P.M. is thankful to the University Grant Commission
(UGC) for funding in the form of Dr. D.S. Kothari post-doctoral research fellowship (Award
no. F4-2/2006 (BSR)/CH/15-16/023). We sincerely thank Department of Chemistry of the
University of Burdwan for infrastructural facilities. K.T. is thankful to the University Grant
Commission (UGC), Eastern Region, Kolkata for funding in the form of UGC minor research
project (Project number PSW-038/14-15(ERO) dated. 03.02.2015). We acknowledge
Department of Science and Technology (DST) and University Grant Commission (UGC)
New Delhi, India for providing support to the Department of Chemistry, University of
Kalyani under PURSE, FIST and SAP program
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Research Highlights
1. A new polymer anchored zinc complex catalyst, PS-Zn-anthra complex, has been
synthesized and characterized.
2. The PS-Zn-anthra complex is stable upto 430 oC using thermogravimetric analysis.
3. The PS-Zn-anthra complex showed excellent catalytic activity for the synthesis of
cyclic carbonates from epoxides with CO2 .under atmospheric pressure and at room
temperature.
4. The PS-Zn-anthra complex also showed good activityfor the synthesis of dicoumarols
under greener pathway.
5. The catalyst is stable and reusable for several cycles without losing its catalytic
activity.